Tunnel tube concrete lining in loose rock - has fluid concrete pressed into annular gap at pressure above rock pressure

A tube is driven forward, a following support structure (5) is introduced, and a connecting annular gap between this and the rock is filled with a fluid substance, in providing concrete lining for a tunnel, esp. in loose rock. The filling substance is fluid support lining concrete pressed into the gap. Concreting pressure is applied such as to build up a hydrostatic pressure exceeding that of the rock. The pressure is maintained by interpolation of control elements which stabilise it. Uses can be made of concrete which expands on setting hard. Lining is evenly and reliably embedded round the entire periphery, with surrounding rock prestressed and all stresses absorbed.